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Ignitable Liquid Residue (ILR)

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What is Ignitable Liquid Residue?

Ignitable liquid residue (ILR) is the evidence left behind at the scene of a fire. ILR represents the portion of an ignitable liquid that did not burn during a fire. ILR is different from an accelerant, which implies intent to start a fire. A scientist will be able to determine if ILR is present based on chemical analysis, while information from the scene can help to determine how that ILR was used or why it might be present at the scene. The simple presence of ILR at the site of an arson investigation does not necessarily mean that the fire was deliberately started.

ILRs that are typically found in structural or wildfire/bushfire arson investigations are primarily petroleum based, such as gasoline, diesel, and lighter fluid. There are many different types of ignitable liquids that may be encountered in arson investigations; however, gasoline is the most common ignitable liquid. Other types of ILRs and their relative prevalence in positive samples are listed in Figure 1, along with a typical example of the chemical fingerprint generated by comprehensive two-dimensional gas chromatography (GC×GC).

Prevalence of ILR types identified in positive samples across Canada

Figure 1. Prevalence of ILR types identified in positive samples across Canada. From Sandercock, P. M. L. (2017). “A survey of fire debris casework in Canada, 2011–2016.” Canadian Society of Forensic Science Journal 51(1): 26-37.

ILRs are identified and classified based on their chemical composition, carbon numbers, and boiling point range. The chemical signatures of different ILR types can be seen in the 3D-image plots generated by GC×GC analysis in Figure 2.

ILR analysis by comprehensive two-dimensional gas chromatography.

Figure 2: ILR analysis by comprehensive two-dimensional gas chromatography (GCxGC).

What are they used for?

Ignitable liquids have many everyday uses, such as fuel for vehicles or other machinery, cleaning products, painting products, solvents, and many others. ILR provides a fingerprint of the ignitable liquid that may have been used to start a fire. This ILR fingerprint is used to determine the presence or absence of an ignitable liquid and can also be used to determine what type of ignitable liquid was used. Definitive detection of ILR in fire debris can influence guilty and non-guilty verdicts in court proceedings and payments for insurance claims. In certain cases, the ILR fingerprint can be linked to a specific source, such as to a specific gas station, or linked to other evidence collected during the investigation (e.g. jerry can and clothing). Chemistry Matters and its analytical partners have accomplished this by using an advanced analytical technique, comprehensive two-dimensional gas chromatography (GC×GC).

  • Legal Sampling
  • Chain of Custody
  • Study Design
  • Data Analysis and Visualization
  • Data Wrangling
  • Multivariate Statistical Analysis
  • Principal Component (PCA); Hierarchical Cluster (HCA)
  • Science Communication
  • Data Science/Big Data
  • GC×GC Analysis
  • Chemical Fingerprinting
  • Clandestine Labs
  • Arsonous Wildfires

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Chemistry Matters Consulting Services and Expertise

Deliberately caused fires can cause significant damage to property, to the environment, as well as the potential loss of human and animal life. As long as arson continues to be a major crime, suspicious fire scenes will continue to be investigated. For successful prosecutions to occur, the highest level of scientific expertise is required to interpret the evidence. The Chemistry Matters team is well suited to assist in these endeavours. We have the experience to aid in the proper sample collection and legal chain of custody documentation of evidence at fire scenes to meet litigation scrutiny. We have the litigation experience required for expert witness testimony and are actively involved in arson related research by publishing in peer-reviewed journal articles and presenting at scientific conferences.

Arsonous Wildfires

Arson investigations are not limited to buildings and property – arsonous wildfires (bushfires) account for a large portion of wildfires each year. Human-caused wildfires represent substantial economic costs and ecological losses across the globe. While some human caused fires may be due to inadvertent activity (e.g. all-terrain vehicles (ATVs)), others are deliberately started. Suspected arsonous wildfires in which the use of an accelerant is suspected are complex investigations due, in part, to the high abundance of natural background chemicals and the lower volume of ignitable liquid being applied over a larger area.

Given the complex nature of forest fire debris, wildfire samples require advanced analytical techniques that are not included in standard methods. Chemistry Matters is pioneering the application of comprehensive two-dimensional gas chromatography with time of flight mass spectrometry (GC×GC-TOFMS) to wildfire investigations. GC×GC enables superior separation of hundreds of ILR chemicals from complex co-extracted matrix chemicals in wildfire debris samples and also provides a more sensitive detection limit. Therefore, we can identify more chemicals at lower concentrations than ever before. GC×GC-TOFMS is able to differentiate ILR at lower concentrations after longer burning times than conventional GC analysis, as shown in Figure 3.

Wood chips spiked with gasoline burnt for the specified time. Top: Conventional GC-MS analysis. Bottom: GCxGC-TOFMS analysis.
Figure 3: Wood chips spiked with gasoline burnt for the specified time. Top: Conventional GC-MS analysis. Bottom: GCxGC-TOFMS analysis.

Property Fires

Property fires are the most common type of arson investigation, which includes commercial and residential structures, as well as vehicles. Arson is also often used to conceal other criminal activity. Collecting and preserving evidence is of paramount importance in order to preserve the ILR signal. Ignitable liquids by their very nature are volatile substances, meaning they can easily evaporate if not handled properly. The substrates found in property fires, such as carpet and other textiles, can cause their own interferences, called pyrolysis products, that must be differentiated from the ILR signal. Internationally recognized standard methods from the American Society for Testing and Materials are followed for the analysis of fire debris samples, specifically ASTM E1412 and ASTM E1618. Along with the ASTM methods, Chemistry Matters uses in-house and international databases of ignitable liquids and substrates to interpret the chemical signature(s) present in fire debris samples.

Sample Integrity

The chemical properties of ignitable liquids that make them so attractive to arsonists may also present a series of challenges for sample collection. Ignitable liquids are highly volatile, meaning they evaporate quickly. They are also susceptible to dilution from fire suppression efforts (i.e. water, foam) as well as microbial degradation, either in soils or in improperly preserved samples. Proper sample collection and storage techniques are essential to ensuring sample integrity. Chemistry Matters can provide standard operating procedures specific to each arson investigation in order to maintain sample integrity as well as a legal chain of custody.

Expert Witness

Chemistry Matters Inc. has provided full-service support from evidence collection to expert witness testimony for criminal and civil arson investigations and have been qualified as experts for the courts. The Chemistry Matters team is actively involved in publishing research in peer-reviewed journals that highlight the advantages of using GC×GC-TOFMS compared to conventional GC-MS in litigious investigations. In addition, effective communication of complex scientific findings to non-scientific stakeholders is critical to the success of any legal case. Visual communication is an effective means at describing results to a broad audience. Chemistry Matters use of GC×GC plots and statistical analysis to provide compelling visuals that can be understood by attorneys, judges, regulators, and the general public.

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